Directional drilling describes a commonly used technique for drilling a non-linear wellbore. This type of wellbore is generally characterized by a bottomhole location which is not directly below the surface location of the wellbore, and numerous variations and geometric shapes may be utilized. Directional drilling technology is highly utilized in the production of oil and gas, especially in offshore environments where multiple wells are drilled from one central surface location such as an offshore platform. This technology is extremely cost effective since multiple wellbores can be drilled from one central structure as opposed to constructing platforms for each individual wellbore. Further applications include drilling below populated urban areas, mountainous terrain and other locations where it is either impractical or economically unfeasible to have a surface location directly above a bottomhole location.
Due to the ever increasing difficulty in finding new oil and gas reserves, directional drilling provides a means for oil and gas producers to exploit these energy resources in downhole locations previously unobtainable. However, with increasingly difficult subsurface locations, it is critical that accurate measurements and controls be utilized to properly steer the direction of the wellbore during drilling, especially with increasingly complicated wellbore geometric shapes. Thus, it is increasingly important to oil and gas producing companies to be able to accurately control the directional drilling of a wellbore to accurately reach a target bottomhole location. Further, properly designed and drilled wellbores may eliminate or severely reduce unwanted doglegs and other problematic wellbore configurations that can become troublesome during the completion of the well.
The drilling of a non-vertical, deviated wellbore requires frequent measurement of the downhole location of the drill bit and or other hardware typically referred to as the "bottomhole assembly". The bottomhole assembly may include adjustable stabilizers and various other tools which may be adjusted during the drilling of the well to steer or otherwise orient the direction the well will be drilled.
The current position of the bottomhole assembly is generally determined with measurement while drilling (hereinafter "MWD".) equipment. This equipment allows critical information to be transmitted to the surface location at periodic time or depth intervals, and is used to calculate the coordinates of the current position of the bottomhole assembly. This information is then compared to previous positions of the bottomhole assembly by graphically plotting the actual wellbore path in comparison and to the preferred or projected drilling plan. The preferred drilling plan provides a blueprint of the optimum wellbore path. Based on this information, the present method used to directionally drill a wellbore requires a directional drilling engineer or technical consultant (hereinafter "directional driller") to make adjustments to the position of one or more tools used in the bottomhole assembly to properly steer the direction of the bottomhole assembly and thus the wellbore. Wellbore information which is most commonly used by the directional driller includes only horizontal and vertical deviations as plotted on sectional and plan views and compared to the preferred wellbore path. Modifications to the drillstring bottomhole assembly are then subjectively made based on prior experience.
The limitations of the present method for drilling a directionally deviated wellbore are directly related to human skill and the unavoidable variabilities thereof and the costs related therein. For example, directional drillers have different degrees of education, on site training and expertise, and there is little consistency between any two drillers and their thought processes for accurately making decisions to control the path of the wellbore. Additionally, decisions are commonly made during periods of sleep deprivation which inherently make the decision making process susceptible due to errors in judgment. Further, the necessity of having an onsite directional driller on location, in addition to the rig driller, is expensive just based on their salary. Thus, very costly errors are often made which result in downtime on a drilling rig, the sidetracking of a well due to severe deviations in the wellbore path, and/or the necessity for drilling an entirely new wellbore. Thus, there is a significant need for an automated, numeric control system which can accurately and automatically interpret substantial volumes of data related to an existing position of a wellbore and a preferred wellbore path and make specific corrections to the position of a downhole tool assembly. These corrections in the downhole tool assembly are then used to steer the bottomhole assembly and resultant wellbore path to a desired location while eliminating the substantial risk of human error.
Thus, a significant need exists to provide a numerical control unit for wellbore drilling which can process substantial amounts of constantly changing data related to the current position of a wellbore and a preferred position of a wellbore. This information may then be used to accurately dictate the required change in the positional settings of a downhole adjustable tool to properly steer a bottomhole assembly to a desired target location. Reliable, automated directional drilling of the future unquestionably requires such.